Switch-mode AC-DC regulator enables ultra-low standby power in USB chargers

Latest from Diodes Incorporated, the AP3785T AC-DC primary-side switched-mode power supply controller is aimed at 8W to 15W 5V output USB chargers that necessitate ultra-low standby power. This market requirement is driven by smart phones and tablets with larger battery capacities and increasingly tight power supply efficiency regulations. Offered in a small, standard pinout, SO-8 package, the AP3785T offers various features which contribute to its superior performance : a no-load input power rating of less than 10mW; higher efficiency and better EMI result from valley-on operation and a low VCS jitter specification; higher conversion efficiency is also achieved when the AP3785T is used in conjunction with a synchronous rectifier, such as the AP4341. Multiple PWM/PFM control modes further help improve audio noise and efficiency. Over-voltage protection, output short-circuit protection and transformer saturation protection (via primary peak-current limitation) are all built into the AP3785T. Internal temperature protection is also provided along with a dedicated pin to support external temperature protection. When operating as a constant current regulator, a feedback pin enables compensation for changes in line voltage whereas in constant voltage mode the AP3785T can compensate for voltage drops due to different cable lengths or gauge.